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Interacting Dirac magnons in the van der Waals ferromagnet CrBr3

Saikat Banerjee1,2,* and Stephan Humeniuk2,†

  • *Contact author: saikat.banerjee@uni-greifswald.de
  • †Contact author: stephan.humeniuk@gmail.com
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Phys. Rev. B 112, 094407 – Published 4 September, 2025

DOI: https://doi.org/10.1103/llz4-5k6g

Abstract

We study the effects of magnon-magnon interactions in the two-dimensional van der Waals ferromagnet CrBr3 focusing on its honeycomb lattice structure. Motivated by earlier theoretical predictions of temperature-induced spectral shifts and van Hove singularities in the magnon dispersion [S. S. Pershoguba et al., Phys. Rev. X 8, 011010 (2018)], we go beyond the commonly used thermal magnon approximation by applying second-order perturbation theory in a fully numerical framework. Our analysis uncovers significant deviations from previous analysis: in particular, the predicted singularities are absent, consistent with recent inelastic neutron scattering measurements [S. E. Nikitin et al., Phys. Rev. Lett. 129, 127201 (2022)]. Moreover, we find that the temperature dependence of the renormalized magnon spectrum exhibits a distinct T3 behavior for the optical magnon branch, while retaining T2 behavior for the acoustic or down magnon band. This feature sheds light on the collective dynamics of Dirac magnons and their interactions. We further compare the honeycomb case with a triangular Bravais lattice, relevant for ferromagnetic monolayer MnBi2Te4, and show that both systems lack singular features while displaying quite distinct thermal trends.

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Phys. Rev. B 112, 094407– Published 4 September, 2025
  • Received 9 June 2025
  • Revised 30 July 2025
  • Accepted 19 August 2025
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